Coffee

Based on how often you get to practice, you can get the hang of it within a day or two, but even my slower colleagues got it after a few weeks.

• Milk consistency helps a lot: freshly steamed milk is always easier to "draw" with; burnt or 3 times re-heated milk is pretty hard to move around. The smaller the bubbles in the milk, the nicer shapes you can make, so make sure you steam it juuuuust close enough to the surface (but still in the milk) so that it can still make nice and small bubbles. Like when you blow your snotty nose. EDIT: Also, you don't need to make it 100% foam. That actually makes it somewhat harder. It should be fine as long as the foam is about ~5-20% of the total jug milk height.
• The magic circles over the milk is not just a flashy show: when they do that, they actually try to form the "base" for the milk. They make a thin layer of foam distributed evenly first, so that when they start to "draw", it will nicely spread on the surface instead of going everywhere on a watery base.
• When making the "base" for the art, try to tilt the cup a bit so that one part of the hot milk is a bit more shallow (closer to the bottom bit of the rim). I like to tilt it enough so that it's almost at the very edge, and as I start pouring later, I slowly tilt it back, closer to level, because as you pour the milk you also fill the cup. So you do this tilt bit because the foamy milk you pour in will have an easier time to slow down and "sit up" on the surface, as opposed to zooming through it, breaking the film and ending up on the bottom.
• For the single heart (which is the best to start with for the simplicity and because the tulip is just several hearts), you should start pouring the milk at the shallow bit, preferably reeeeally close to the rim where the cup is almost spilling. Not just the milk, but the jug, too: they can even touch with the cup. As you start pouring from the jug, you adjust the tilt with the other hand, otherwise you'll need to clean your shoes. Don't be too slow: it needs to make space for itself in the foam layer. Don't be too fast: if you pour from too far above, it will just jump dive through the foam layer without sticking to it and make a hole (without much white). It should start to form a circle.
• Around the time you think it's an okay size (and there's half a cup of hot milk on your trousers), you can do the finishing move. Start close to the surface with the jug (as it was supposed to be there all along), and as you move it forward (closer to the centre of the cup), lift it up gradually. Ideally, after a few attempts it should look like a smooth semi-circular motion forward and up. Do it too fast and it will stay a circle because the pouring milk gets too thin and too fast to draw; do it too slow and it will elongate it a bit too much.
• Just remember that the closer you are, the thicker your "brush" is; the higher up, the thinner it is until it's too fast and/or thin to properly draw with. Also, the closer you are and the slower you pour, the more connected your shape gets with the jug through the slow, surprisingly sticky foam, therefore you will both morph the edges and also move the shape as it sticks to the short foam bridge. This is what we can use for two things: making the apex of the heart by morphing it less and less as you pull away from it, resulting in a nice, narrowing end (and also creating the top middle ridge) and this is how you...
• move the shape: just stay close to the centre as you pour it, and as you push the jug forward closely above the milk, it will push your heart closer to the centre of the cup so that it doesn't look like it is about to sneak out of the cup.

All in all, you will still have to practice to feel the amount you can control size, thickness, speed etc., but it's easier when you know what's going on in the cup.

Have a lot of fun practicing and I wish you a lot of round hearts! Also, don't be ashamed: everyone starts out with gourds, dicks and butts. At least you can say it was intentional.